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rpc.mountd(8)                                                    rpc.mountd(8)

       rpc.mountd - NFS mount daemon

       /usr/sbin/rpc.mountd [options]

       The  rpc.mountd daemon implements the server side of the NFS MOUNT protocol, an NFS
       side protocol used by NFS version 2 [RFC1094] and NFS version 3 [RFC1813].

       An NFS server maintains a table of local physical file systems that are  accessible
       to  NFS clients.  Each file system in this table is referred to as an exported file
       system, or export, for short.

       Each file system in the export table has an access control list.   rpc.mountd  uses
       these  access  control  lists  to  determine  whether an NFS client is permitted to
       access a given file system.  For details on how to manage your NFS server's  export
       table, see the exports(5) and exportfs(8) man pages.

   Mounting exported NFS File Systems
       The NFS MOUNT protocol has several procedures.  The most important of these are MNT
       (mount an export) and UMNT (unmount an export).

       A MNT request has two arguments: an explicit argument that contains the pathname of
       the  root  directory  of the export to be mounted, and an implicit argument that is
       the sender's IP address.

       When receiving a MNT request from an NFS client, rpc.mountd checks both  the  path-
       name  and  the sender's IP address against its export table.  If the sender is per-
       mitted to access the requested export, rpc.mountd returns an NFS  file  handle  for
       the  export's  root directory to the client.  The client can then use the root file
       handle and NFS LOOKUP requests to navigate the directory structure of the export.

   The rmtab File
       The rpc.mountd daemon registers every successful MNT request by adding an entry  to
       the  /var/lib/nfs/rmtab  file.   When  receivng  a UMNT request from an NFS client,
       rpc.mountd simply removes the matching entry from /var/lib/nfs/rmtab,  as  long  as
       the access control list for that export allows that sender to access the export.

       Clients can discover the list of file systems an NFS server is currently exporting,
       or the list of other clients that have mounted its  exports,  by  using  the  show-
       mount(8)  command.  showmount(8) uses other procedures in the NFS MOUNT protocol to
       report information about the server's exported file systems.

       Note,  however,  that  there  is  little  to  guarantee  that   the   contents   of
       /var/lib/nfs/rmtab  are  accurate.   A client may continue accessing an export even
       after invoking UMNT.  If the client reboots without sending a UMNT  request,  stale
       entries remain for that client in /var/lib/nfs/rmtab.

       -d kind  or  --debug kind
              Turn on debugging. Valid kinds are: all, auth, call, general and parse.

       -F  or  --foreground
              Run in foreground (do not daemonize)

       -f export-file  or  --exports-file export-file
              This option specifies the exports file, listing the clients that this server
              is prepared to serve and  parameters  to  apply  to  each  such  mount  (see
              exports(5)).  By default, export information is read from /etc/exports.

       -h  or  --help
              Display usage message.

       -o num  or  --descriptors num
              Set  the limit of the number of open file descriptors to num. The default is
              to leave the limit unchanged.

       -N mountd-version  or  --no-nfs-version mountd-version
              This option can be used to request that rpc.mountd do not offer certain ver-
              sions of NFS. The current version of rpc.mountd can support both NFS version
              2, 3 and 4. If the either one  of  these  version  should  not  be  offered,
              rpc.mountd must be invoked with the option --no-nfs-version <vers> .

       -n  or  --no-tcp
              Don't advertise TCP for mount.

       -p num  or  -P num  or  --port num
              Specifies  the port number used for RPC listener sockets.  If this option is
              not specified, rpc.mountd chooses a random ephemeral port for each  listener

              This option can be used to fix the port value of rpc.mountd's listeners when
              NFS MOUNT requests must traverse a firewall between clients and servers.

       -H  prog or  --ha-callout prog
              Specify a high availability callout program.  This program receives callouts
              for  all MOUNT and UNMOUNT requests.  This allows rpc.mountd to be used in a
              High Availability NFS (HA-NFS) environment.

              The callout program is run with 4 arguments.  The first is mount or  unmount
              depending on the reason for the callout.  The second will be the name of the
              client performing the mount.  The third will be the path that the client  is
              mounting.   The  last is the number of concurrent mounts that we believe the
              client has of that path.

              This callout is not needed with 2.6 and later kernels.  Instead,  mount  the
              nfsd filesystem on /proc/fs/nfsd.

       -s, --state-directory-path directory
              Specify  a  directory  in  which  to place statd state information.  If this
              option is not specified the default of /var/lib/nfs is used.

       -r, --reverse-lookup
              rpc.mountd tracks IP addresses in the rmtab file.  When a  DUMP  request  is
              made  (by  someone  running  showmount  -a,  for  instance),  it  returns IP
              addresses instead of hostnames by default. This option causes rpc.mountd  to
              perform  a  reverse  lookup  on  each  IP  address  and return that hostname
              instead.  Enabling this can have a substantial negative  effect  on  perfor-
              mance in some situations.

       -t N or --num-threads=Nor --num-threads N
              This  option  specifies the number of worker threads that rpc.mountd spawns.
              The default is 1 thread, which is probably enough.  More threads are usually
              only needed for NFS servers which need to handle mount storms of hundreds of
              NFS mounts in a few seconds, or when your DNS server is slow or  unreliable.

       -V version  or  --nfs-version version
              This option can be used to request that rpc.mountd offer certain versions of
              NFS. The current version of rpc.mountd can support both NFS  version  2  and
              the newer version 3.

       -v  or  --version
              Print the version of rpc.mountd and exit.

       -g  or  --manage-gids
              Accept  requests from the kernel to map user id numbers into  lists of group
              id numbers for use in access control.  An NFS request will normally  (except
              when  using Kerberos or other cryptographic authentication) contains a user-
              id and a list of group-ids.  Due to a limitation in  the  NFS  protocol,  at
              most  16 groups ids can be listed.  If you use the -g flag, then the list of
              group ids received from the client will be replaced by a list of  group  ids
              determined  by  an appropriate lookup on the server. Note that the 'primary'
              group id is not affected so a newgroup command on the client will  still  be
              effective.   This  function  requires  a  Linux Kernel with version at least

       You can protect your rpc.mountd listeners using the tcp_wrapper  library  or  ipta-

       Note that the tcp_wrapper library supports only IPv4 networking.

       Add  the  hostnames  of  NFS  peers  that  are  allowed  to  access  rpc.mountd  to
       /etc/hosts.allow.  Use the daemon name mountd even if the rpc.mountd binary  has  a
       different name.

       Hostnames  used in either access file will be ignored when they can not be resolved
       into IP addresses.  For further information see the tcpd(8) and hosts_access(5) man

   IPv6 and TI-RPC support
       TI-RPC  is  a pre-requisite for supporting NFS on IPv6.  If TI-RPC support is built
       into rpc.mountd, it attempts to start listeners on network transports marked 'visi-
       ble'  in /etc/netconfig.  As long as at least one network transport listener starts
       successfully, rpc.mountd will operate.

       /etc/exports             input file for exportfs, listing exports, export  options,
                                and access control lists

       /var/lib/nfs/rmtab       table of clients accessing server's exports

       exportfs(8),   exports(5),   showmount(8),   rpc.nfsd(8),  rpc.rquotad(8),  nfs(5),
       tcpd(8), hosts_access(5), iptables(8), netconfig(5)

       RFC 1094 - "NFS: Network File System Protocol Specification"
       RFC 1813 - "NFS Version 3 Protocol Specification"

       Olaf Kirch, H. J. Lu, G. Allan Morris III, and a host of others.

                                  31 Dec 2009                    rpc.mountd(8)

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